The complete or partial detachment of ligaments, tendons or other soft tissues (hereinafter “ligamentary material”) from the bones with which they are associated are commonplace, particularly among athletes. Such injuries usually result from excessive stress being applied on these tissues. Some degree of tissue detachment may occur, for instance, as the result of an accident, overexertion during a work-related activity, stress during the course of an athletic event, or in conjunction with numerous other situations and activities. If, however, ligamentary material is completely detached from its associated bone(s) or is severed, partial or permanent disability may result.
Fortunately, there are numerous surgical techniques known and used in the art for reattaching detached tissues and/or completely replacing ligamentary material. One such technique involves the use of “traditional” fasteners (e.g. metal staples, cancellous bone screws.) Such fasteners have also been used to attach tendon or ligament substitutes (often formed of autogenous tissue harvested from elsewhere in the body, collectively referred to herein as “grafts” or “graft material”) to the desired bone(s). A common surgery involves replacing or repairing the anterior cruciate ligament (ACL) in a human knee. Bone tunnels are appropriately aligned and formed in both the proximal tibia and the distal femur during the course of this surgery. Graft material is somehow rigidly coupled, usually with bone blocks to be inserted into these tunnels, to fix the material in a proper position for long term use in the body.
Such ligament fixation schemes have not been entirely successful. For example, rigid attachment using “traditional” attachment devices such as staples, sutures and screws often cannot be maintained even under normal tensile loads. Also, the use of sharp screws to create a locking interference fit between a bone plug/block and a bone tunnel may be problematic. For instance, there is always the possibility of damaging the ligament during insertion of the screw. In addition, it may be difficult to maintain the desired tension on the graft material during insertion of the screw. Alternative, non-rigid fixation schemes (such as suspending a ligament graft from a suture button) also have drawbacks. Because the graft structure is not, in such schemes, rigidly fixed within the bone tunnels, movement of the graft structure may disrupt the healing process. It is known that intimate contact between the graft material and the walls of the bone tunnels aids in ensuring an effective, efficient healing process.
Another potential problem may arise even where the graft material appears to be successfully fixed within the bone tunnel. Bone tunnels are usually drilled for a considerable length into the femur for fixation of the graft material in ACL replacement procedures. Where exactly within the tunnel the graft is fixed often depends on the manner of fixation and tensioning of the graft material, but often the site for fixation is chosen as the place where the fixation device best allows fixing. Where the fixation takes place inside the bone tunnel apart from the bone tunnel edge at the distal end of the femur, the graft material that extends from the fixation point to the edge of the bone tunnel often moves or slides within this remaining portion of the tunnel. This phenomenon is known to some surgeons as the “windshield wiper” effect. As noted above, movement tends to prevent healing and fixation of the soft tissue to bone, so where the windshield wiper effect occurs, the portion of the graft that moves when the patient uses the reconstructed joint may never heal completely in the region near the edge of the bone tunnel. This potential problem defeats the goal of most surgeons which is to have the graft material fix as close as possible to its natural fixation point before being damaged by injury or disease. This natural fixation point is generally at the edge of the bone tunnel, where the graft will not fix if the windshield wiper effect is present.
Accordingly, there is a need for ligament graft fixation devices that reliably provide fixation of graft material in the region closest to the natural fixation point of the ligamentary material being replaced.